Abstract:

The coded wire tag (CWT) database contains detailed information on millions of Pacific salmon
Oncorhynchus spp. released from hatcheries or smolt traps and recovered in the north Pacific Ocean and its tributaries. I used this data set to examine the spatial and temporal variation in the marine distributions of 77 hatchery and 16 wild populations of Chinook salmon O. tshawytscha based on recoveries of an estimated 632,000 tagged salmon in coastal waters from southern California to the Bering Sea during 1979–1994 (and 1995–2004 for select hatcheries). Chinook salmon showed 12 distinct region-specific recovery patterns. Chinook salmon originating in a common freshwater region had similar marine distributions, which were distinct from those of adjacent regions. Different run types (e.g., spring, summer, and fall runs) originating in the same region exhibited variation in their marine distributions consistent with recovery at different stages of their ocean residence period. Recovery patterns were surprisingly stable across years, despite high interannual variation in ocean conditions. By contrast, ocean age influenced recovery patterns, as older fish were recovered further from their natal stream than younger fish. Although most of the CWT data used in the analysis came from hatchery fish, recoveries of tagged wild populations indicate patterns similar to those of fish from nearby hatcheries. The consistency in these findings across broad geographic areas suggests that they apply to Chinook salmon across the entire Pacific Rim. Similar findings for tagged coho salmon O. kisutch indicate that the observed patterns may apply to Pacific salmon as a whole and provide a model for other highly migratory fishes that have not benefited from such intensive tagging programs. The results also have implications for the genetic control of migration and salmon’s ability to respond to climate change.